Openhab2 Designer - Error flagging of actions in rules configuration

Being in the process of migrating from OH 1.8.3 to OH 2.0.0 I noticed that in the OH2 designer (using it on Windows 10 and Debian Linux 32bit version) actions that had been validated properly are now flagged with errors.

OH2 Designer complains that e.g. in one rule the action

val String XBMC_LIVING = ""
val Integer XBMC_PORT = 80
sendXbmcNotification(XBMC_LIVING, XBMC_PORT, "Haussteuerung deaktiviert", "Openhab 2.0.0")

lacks a definition: The method sendXbmcNotification(String, Integer, String, String) is undefined

I tried to put the org.openhab.action.xbmc-1.9.0.jar file into the ${OH2_DESIGNER_HOME}/addons directory as it was recommended in the Designer 1.x.x series, but this did not solve the problem (neither after restarting the designer).

The rule however executes fine in the OH2 runtime.

What do I need to do in order to get rid of this error flagging in OH2 Designer?
Am I missing a considerable aspect?

This is a known and yet unresolved limitation/bug. No workaround.